Creating an Interactive Prompt in C++

There are multiple ways to solve this and it's debatable what the "right" solution is. If I were to solve it for my own work, I would create a table of a custom struct. Something like:

struct CommandStruct { char *command; int (*commandHandler)(/*params*/); } commandTable[] = { { "tick", tickCommand }, { "start", startCommand }, ... }; 

Then my processing loop would walk through each element of this table, looking for the right match, such as:

for (int i = 0; i < TABLE_SIZE; ++i) { if (command == commandTable[i].command) { /* using whatever proper comparison is, of course */ commandTable[i].commandHandler(/*params*/); break; } } 

Not really a pattern, but often a good approach:

#include <map> #include <functional> #include <string> #include <iostream> typedef std::map< std::string, std::function<void(void)> > command_dict; // ^^^^^^^^ // the signature of your commands. probably should have an error code. void command1() { std::cout << "commanda" << std::endl; } void command2() { std::cout << "commandb" << std::endl; } void command3() { std::cout << "commandc" << std::endl; } int main() { command_dict c; c["a"] = &command1; c["b"] = &command2; c["c"] = &command3; std::string input; while(std::getline(std::cin, input)) { // quit the program with ctrl-d auto it = c.find(input); if(it != end(c)) { (it->second)(); // execute the command } else { std::cout << "command \"" << input << "\" not known" << std::endl; } } } 

The if-else ladder is fine.

It can in principle be replaced with a map<string, Function>, but that gains you nothing for this concrete case (it is added complexity for no particular gain, even with a high number of commands).

When I wrote this initially I forgot to mention though:

• Make your command handlers separate functions.

If you don’t, then the if-else ladder can become quite messy… The map solution requires separate functions, and can therefore appear to be a little more clean than an everything-directly-here if-else ladder. But it’s really the separate functions that then provide a measure of clarity, while the map detracts a little (adding extra work in maintaining the map, and an extra level of indirection to cope with).

On the other hand, since “read commands from the console” indicates interactive input, with a user in the picture, you don’t want to read two or more commands from the same line of input. Because that would screw up the prompting, and can seem quite baffling to the user. So instead of reading a “word” of input at a time using >>, use std::getline to a read a full line of input at a time.